Recipient Organization
UNIV OF WISCONSIN
21 N PARK ST STE 6401
MADISON,WI 53715-1218
Performing Department
Biological Systems Engineering
Non Technical Summary
Corn stover is an abundant source of biomass that can be utilized for bioenergy production, representing 70% of the available crop residues in the U.S. However, recent projections estimate that over 60% of corn stover will be collected at moisture levels that exceed 20%. This is incompatible with conventional dry harvest and storage systems due to unwanted microbial degradation. For 40% of the stover that could be utilized with the current technology, multiple other technical challenges exist. The result is a persistent lack of ability to produce a reliable feedstock. Consequently, there are no real existing markets for cellulosic material beyond on-farm use.An alternative to dry bale storage is an anaerobic storage process, also known as ensiling. An anaerobic or oxygen-limiting environment promotes lactic acid bacteria to ferment soluble sugars into organic acids, thereby reducing the substrate pH and preserving the biomass from microbial degradation. Ensiling processes benefit from wetter corn stover but have also demonstrated utility for moist (~25 - 40% moisture) crop. Wet or moist anaerobic storage can accommodate both chopped and bale formats. Ensiling is employed widely in the livestock, pulp and paper, and sugar cane industries to preserve biomass.Could we reimagine a biomass harvest, transport, and storage system that would leverage the advantages of the state of the art?The central hypothesis of our research is that the lowest-cost, highest-quality corn stover will result from single-pass harvest, anaerobic storage of moist whole-plant corn (grain and stover), co-transport, and grain fractionation at the biorefinery gate. Our objectives are to (1) develop a harvest system that can separate corn ears from stover, size reduce stover and then recombine the two fractions for storage, (2) study anaerobic preservation of whole ear corn and chopped stover, and (3) estimate the cost performance of the system.The knowledge developed during this project would be directly applicable to whole-plant corn silage, which is an important feedstock in U.S. dairy and livestock industries. The livestock industry has invested significant technology development to improve utilization of the grain fraction of the plant. The proposed technology would result in a paradigm shift where the grain fraction could be processed independently of fiber.
Animal Health Component
50%
Research Effort Categories
Basic
(N/A)
Applied
50%
Developmental
50%
Goals / Objectives
The goal of this project is to develop technologies and scientific knowledge around a novel harvest and storage strategy that combines chopped stover with single-pass whole-ear harvest, stover size reduction, and storage. Specifically, our objectives are to: (1) develop a harvest system that can separate corn ears from stover, size reduce stover and recombine the two fractions for storage, (2) study anaerobic preservation of whole ear corn and chopped stover, and (3) report the cost performance of the system.
Project Methods
Objective 1. Ear corn and stover harvest system. We envision an ear-corn fractionation system that enables single-pass harvest of corn ears and stover on a self-propelled forage harvester platform. Our initial design concept considers combining an ear-snapper head with a whole plant head. The ear snapper head would be located parallel to the whole-plant head and forward in the direction of travel so that the ears could be removed before stalk capture by the whole-plant head. Our concept will employ a row-sensitive, whole-plant head to minimize header weight.The addition of the ear-snapper header will have a significant impact on harvester productivity as well as the physical and chemical properties of the biomass. During the harvest, we will quantify the material capacity as well as grain loss, and damage. Grain loss will be assessed pre-harvest and after the header, including any grain in the chopped stover. The quotient of these data and the crop yield will determine the harvest losses. Time-motion data will be collected to determine the machine's productivity per area (field capacity) and per unit mass harvested (material capacity). These data will allow estimation of the harvester's operating costs (variable) on a per acre and per unit grain basis. The relationship between crop moisture, harvest speed, and grain loss will be studied in a designed experiment. Objective 2. Study anaerobic preservation of whole ear corn and chopped stover. This objective focuses on the development of knowledge related to the anaerobic storage characteristics of ear corn and stover. Harvested stover and ear corn will be stored anaerobically in 19 L polyethylene buckets with a 0.01 mm low-density polyethylene liner (mini-silos). The mini-silos will be used in a designed experiment to study the impact of independent variables of harvest moisture content, and grain format on response variables of dry matter loss, fermentation products, cell wall composition, and monomeric sugar release.The chemical composition of the corn stover biomass will be determined pre- and post- storage based on industry standard and assessing carbohydrate release using relevant approaches for pretreatment and enzymatic hydrolysis. Dilute acid pretreatment will be employed to depolymerize hemicellulose so that cellulose can be accessed by enzymes. Enzymatic hydrolysis using glycosidases will be conducted to further understand carbohydrate monomerization.Objective 3. Cost performance of the system. We plan to use the field data generated in this work with previously published regional delivery frameworks and stakeholder input to develop a feasible process for delivering corn grain and fractionated stover to a biorefinery. The basic process will be field fractionation of ears and precision chopping of stover. These two streams will be recombined and co-stored anaerobically. The moisture content will be sufficiently low so as to limit fermentation. Consequently, the entirety of the storage structure will be emptied upon need at the biorefinery or regional processing depot. The next processing step will involve fractionation of the ears from the stover and threshing and separating the grain from the husk and cob. Depending on the conversion strategy, the cob and husk can remain separate or can be recombined with the remaining stover stalk and leaf fractions. If a division between high and low recalcitrant feedstock is desired, the equipment at the refinery or depot could be utilized to further fractionate the stover components. Each of these scenarios will be considered.Cost analysis will be used to explore the benefits of these processing options using literature and vendor-supplied equipment costs and standard engineering costing methods to estimate total fixed capital investment. Production costs will be estimated from operating costs (raw material, labor, utilities, maintenance, operating supplies), fixed charges (depreciation of fixed capital), and financing (interest). Preliminary results will be shared with appropriate shareholders to further refine the analysis.Process yield data and capital equipment/processing related costs will be combined with field harvesting data to determine total cost throughout the production system. On-farm and regional process equipment sharing will be considered by balancing capital and transportation costs. Here we plan to use an engineering approach and equations from ASABE Standards EP496.3 and D497.5 to calculate ownership and operating costs per hour of equipment use.